A polycarbonate resin is widely employed for transparent materials for industrial use in the field of e.g. electricity, machines or automobiles, from the viewpoint of its excellent transparency and heat resistance. Further, the polycarbonate resin is also used for e.g. lenses or optical disks as a plastic for optical materials.
In order to further improve the strength of such a polycarbonate resin, it is effective to reinforce it with a glass fiber, and at that time, it is desired to reinforce the fiber without lowering the excellent transparency of the polycarbonate resin itself.
Namely, the refractive index (refractive index by sodium D line: hereinafter referred to as nD) of E glass as an example of usual glass fiber material is approximately 1.555. Whereas, the refractive index of the polycarbonate resin is high at a level of from 1.580 to 1.590. Therefore, if a fiber made of usual E glass is dispersed in a polycarbonate resin, there will be a problem such that the transparency will be lowered by the difference in the refractive index between them.
Accordingly, it has been studied to change the composition of the glass fiber to improve the refractive index to bring it to the same level as the refractive index of a polycarbonate resin thereby to maintain the transparency of a molded product of a glass fiber-reinforced polycarbonate resin.
For example, Patent Document 1 discloses a glass fiber composition to be used for reinforcing a polycarbonate resin, comprising from 50 to 65% of SiO2, from 0 to 6% of Al2O3, from 0 to 5% of MgO, from 3 to 10% of CaO, from 2 to 10% of BaO, from 0 to 7% of ZnO, from 0 to 5% of SrO, from 3 to 8% of Na2O, from 3 to 8% of K2O, from 0 to 5% of LiO, from 3 to 10% of ZrO2 and from 5.3 to 10% of TiO2, as represented by weight percentage.
Further, Patent Document 2 discloses a glass composition to be used for reinforcing a polycarbonate resin, comprising from 54.0 to 62.0% of SiO2, from 8.0 to 12.0% of Al2O3, from 0 to 5.0% of MgO, from 18.0 to 22.0% of CaO, from 0 to 5.0% of BaO, from 0 to 5.0% of ZnO, from 0 to 1.0% of Na2O+K2O+Li2O, from 0.6 to 5.0% of ZrO2 and from 0.5 to 1.9% of TiO2, as represented by weight percentage, and having a refractive index of from 1.5700 to 1.6000.
Further, Patent Document 3 discloses a glass fiber for reinforcing a polycarbonate resin, having optical constants such as a refractive index of from 1.570 to 1.600 and an Abbe number of at most 50.
Further, it has been studied to use a commercially available glass fiber to improve a polycarbonate resin. For example, Patent Document 4 discloses a resin composition comprising an aromatic polycarbonate resin employing, as a terminator, a reaction product of a hydroxyaralkyl alcohol and a lactone, and a glass filler having a difference of at most 0.01 in the refractive index from the aromatic polycarbonate resin.
Further, Patent Document 5 discloses a resin composition comprising an aromatic polycarbonate resin, a glass fiber having a difference of at most 0.015 in the refractive index from the aromatic polycarbonate resin, and polycaprolactone.    Patent Document 1: JP-A-58-60641    Patent Document 2: JP-A-5-155638    Patent Document 3: JP-A-5-294671    Patent Document 4: JP-A-7-118514    Patent Document 5: JP-A-9-165506